1. Field of the Invention
This invention relates generally to semiconductor fabrication technology, and, more particularly, to various methods of controlling wet chemical processes in forming metal silicide regions, and a system for performing same.
2. Description of the Related Art
There is a constant drive within the semiconductor industry to increase the operating performance of integrated circuit devices, e.g., microprocessors, memory devices, and the like. This drive is fueled by consumer demands for computers and electronic devices that operate at increasingly greater speeds. This demand for increased speed has resulted in a continual reduction in the size of semiconductor devices, e.g., transistors. That is, many components of a typical field effect transistor (FET), e.g., channel length, junction depths, gate insulation thickness, and the like, are reduced. For example, all other things being equal, the smaller the channel length of the transistor, the faster the transistor will operate. Thus, there is a constant drive to reduce the size, or scale, of the components of a typical transistor to increase the overall speed of the transistor, as well as integrated circuit devices incorporating such transistors. Moreover, the density of such transistors on a wafer per unit area has dramatically increased as a result of, among other things, the reduction in feature sizes, and an overall desire to minimize the size of various integrated circuit products.
By way of background, modem integrated circuit devices, e.g., microprocessors, ASICs, memory devices, etc., are comprised of millions of field effect transistors formed on a semiconducting substrate, such as silicon. The substrate may be doped with either N-type or P-type dopant materials. An illustrative field effect transistor 10, as shown in FIG. 1, may have a doped polycrystalline silicon (polysilicon) gate electrode 14 formed above a gate insulation layer 16. The gate electrode 14 and the gate insulation layer 16 may be separated from doped source/drain regions 22 of the transistor 10 by a dielectric sidewall spacer 20. The source/drain regions 22 for the transistor 10 may be formed by performing one or more ion implantation processes to introduce dopant atoms, e.g., arsenic or phosphorous for NMOS devices, boron for PMOS devices, into the substrate 11. Shallow trench isolation regions 18 may be provided to isolate the transistor 10 electrically from neighboring semiconductor devices, such as other transistors (not shown). Additionally, although not depicted in FIG. 1, a typical integrated circuit product is comprised of a plurality of conductive interconnections, such as conductive lines and conductive contacts or vias, positioned in multiple layers of insulating material formed above the substrate. These conductive interconnections allow electrical signals to propagate between the transistors formed above the substrate.
The gate electrode 14 has a critical dimension 12, i.e., gate length, that approximately corresponds to the channel length 13 of the device when the transistor 10 is operational. Thus, it is very important that the critical dimension 12 of the gate electrode 14 be formed very accurately. Even small errors in the critical dimension 12 of the gate electrode 14 can result in the failure of the finished product to meet certain target electrical performance characteristics, e.g., switching speed, leakage current, etc. Of course, the critical dimension 12 of the gate electrode 14 is but one example of a feature that must be formed very accurately in modern semiconductor manufacturing operations. Other examples include, but are not limited to, conductive lines, openings in insulating layers to allow subsequent formation of a conductive interconnection, i.e., a conductive line or contact, therein, etc.
Also depicted in FIG. 1 are a plurality of metal silicide regions 17 that are formed above the gate electrode 14 and the source/drain regions 22. In general, one purpose of the metal silicide regions 17 is to reduce contact resistance and thereby enhance various operating characteristics of the transistor 10 and integrated circuit products, e.g., microprocessors, incorporating such transistors 10. The metal silicide regions 17 may be comprised of a variety of different materials, e.g., cobalt silicide, titanium silicide, nickel silicide, platinum silicide, tantalum silicide, tungsten silicide, etc.
The metal silicide regions 17 may be formed by a variety of known techniques. One illustrative process flow for forming the metal silicide regions 17 is depicted in FIGS. 2A-2C. Initially, as shown in FIG. 2A, a layer of refractory metal 21 is deposited above the gate electrode 14 and the source/drain regions 22. Thereafter, one or more anneal processes are performed to convert portions of the layer of refractory metal 21 in contact with the silicon-containing gate electrode 14 and source/drain regions 22 into the metal silicide regions 17, as indicated in FIG. 2B. Then, a wet chemical process is performed to remove unreacted portions of the layer of refractory metal 21, as shown in FIG. 2C.
Referring back to FIG. 1, using current-day technology, the channel length 13 of modem transistors may be approximately 120-180 nm, and further reductions are planned in the future. The reduction in the channel length 13 of the transistor 10 also requires a reduction in the physical size of other components of the transistor 10. For example, the depth of the source/drain regions 22 is also reduced along with the length 12 of the gate electrode 14. As a result of the dramatic reduction of device dimensions, other aspects of the transistor 10 may act to limit the performance characteristics of the transistor. Stated another way, the performance of the transistor 10 may not be limited solely by the channel length 13 of the transistor 10, but rather by the RC-time delay associated with the propagation of electrical signals in an integrated circuit device and within the transistor 10. For example, delays associated with the propagation of an electrical signal along the width, i.e., into the drawing page, of the gate electrode 14 (to turn the transistor xe2x80x9cONxe2x80x9d) may act to limit one or more operating characteristics of the transistor 10. Similarly, signal propagation may be limited through the source/drain regions 22 of the transistor 10. However, the thickness of metal silicide regions 17 on the source/drain regions 22 must be limited so as not to consume too much of the underlying source/drain regions 22 during the formation process.
In some cases, the process parameters used in forming metal silicide regions 17, e.g., anneal temperatures and duration, the duration of wet chemical processes, etc., may be determined by performing various tests on a number of test wafers. In other cases, e.g., removal of unreacted refractory metal 21, a wet chemical process is performed for a duration that is assumed to be sufficient for the maximum anticipated thickness of the originally formed layer of refractory metal 21. However, the duration of the wet chemical process determined using this xe2x80x9cworst casexe2x80x9d type approach may unduly consume other components of the transistor 10 if the layer of refractory metal 21 is thinner than the anticipated xe2x80x9cworst-casexe2x80x9d thickness. For example, depending upon the composition of the material used for the sidewall spacers 20, if the wet chemical process is performed for too long of a duration, it may consume too much of the sidewall spacers 20. As another example, excessive time in the chemical bath may consume some of the metal silicide regions 17.
Additionally, the anneal processes performed to form the metal silicide regions 17 is typically a timed process that is performed for the specified duration set by the particular process flow. Similarly, the wet chemical process performed to remove the unreacted refractory metal is also a timed process. Such fixed, inflexible processing methodologies may inhibit the formation of metal silicide regions 17 exhibiting the desired characteristics. In some cases, such fixed, inflexible processing techniques may result in the production of integrated circuit products that do not exhibit the desired performance characteristics.
The present invention is directed to various methods and systems that may solve, or at least reduce, some or all of the aforementioned problems.
The present invention is generally directed to various methods of controlling wet chemical processes in forming metal silicide regions, and a system for performing same. In one illustrative embodiment, the method comprises providing a substrate having a layer of unreacted refractory metal and at least one metal silicide region formed thereabove, performing a wet chemical process to remove at least a portion of the layer of unreacted refractory metal, measuring at least one characteristic of the portion of the layer of unreacted refractory metal while the wet chemical process is being performed, and controlling at least one parameter of the wet chemical process based upon the measured characteristic of the portion of the layer of unreacted refractory metal.
In another illustrative embodiment, the method comprises providing a substrate having a layer of unreacted refractory metal and at least one metal silicide region formed thereabove, performing a wet chemical process to remove at least a portion of the layer of unreacted refractory metal, measuring at least one characteristic of the portion of the layer of unreacted refractory metal after at least some of the wet chemical process has been performed, and controlling at least one parameter of the wet chemical process based upon the measured characteristic of the portion of the layer of unreacted refractory metal.
In yet another illustrative embodiment, the method comprises providing a substrate having a layer of unreacted refractory metal and at least one metal silicide region formed thereabove, measuring at least one characteristic of at least a portion of the layer of unreacted refractory metal, determining at least one parameter of a wet chemical process to be performed to remove the layer of unreacted refractory metal based upon the measured characteristic, and performing the wet chemical process comprised of the determined parameter on the layer of unreacted refractory metal.
In a further illustrative embodiment, the method comprises providing a substrate having a layer of unreacted refractory metal and at least one metal silicide region formed thereabove, performing a wet chemical process to remove the layer of unreacted refractory metal, measuring at least a thickness of at least a portion of the layer of unreacted refractory metal after at least some of the wet chemical process has been performed, and controlling at least one parameter of the wet chemical process based upon the measured thickness of the portion of the layer of unreacted refractory metal.
In still a further illustrative embodiment, the method comprises providing a substrate having a layer of unreacted refractory metal and at least one metal silicide region formed thereabove, performing a wet chemical process to remove at least a portion of the layer of unreacted refractory metal, measuring a thickness of the metal silicide region at some point after the wet chemical process has been performed, and controlling at least one parameter of the wet chemical process based upon the measured thickness of the metal silicide region.
In yet a further illustrative embodiment, the method comprises providing a substrate having a layer of unreacted refractory metal and at least one metal silicide region formed thereabove, performing a wet chemical process to remove at least a portion of the layer of unreacted refractory metal, measuring a thickness of the metal silicide region at some point after the wet chemical process has been performed, and performing the wet chemical process for a fixed duration after the measured thickness has reached a preselected value.